Modern computer user interfaces make use of multiple application layers in order to present to the user a richer content. These application layers used during screen composition are generated by the active applications. One application may create one or more layers. For example, user interface designers may prefer certain windows or portions of windows to be semi-transparent for both aesthetic and functional reasons. An example of an aesthetic benefit is enabling a user to view at least some of a background layer through a portion of a foreground layer, which enhances the look and feel of the user interface. An example of a functional benefit is enabling a user to view information from a background layer through a portion of a foreground layer, which would otherwise be obstructed by the foreground layer.
In these cases, certain pixels (e.g., those that appear semi-transparent) of the user interface composition include pixel data from more than one application. The amount of pixel data that is required to be read from and written to memory by various system components increases with the number of applications that contribute to a particular user interface composition. Additionally, the desire for increasingly-high refresh rates and screen resolutions place a further burden on the amount of pixel data that is read from and written to memory. Power consumption is a function of the amount of pixel data required to be read from and written to memory and, as a result, power consumption increases and memory bandwidth becomes a limiting factor.